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The effect of spatial resolution on optical and near-IR studies of stellar clusters: implications for the origin of the red excess

Bastian, N and Adamo, A and Schirmer, M and Hollyhead, K and Beletsky, Y and Carraro, G and Davies, B and Gieles, M and Silva-Villa, E (2014) The effect of spatial resolution on optical and near-IR studies of stellar clusters: implications for the origin of the red excess. Monthly Notices of the Royal Astronomical Society, 444 (4). pp. 3829-3836. ISSN 0035-8711

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Abstract

Recent ground-based near-IR (NIR) studies of stellar clusters in nearby galaxies have suggested that young clusters remain embedded for 7–10 Myr in their progenitor molecular cloud, in conflict with optical-based studies which find that clusters are exposed after 1–3 Myr. Here, we investigate the role that spatial resolution plays in this apparent conflict. We use a recent catalogue of young (<10 Myr) massive (>5000 M⊙) clusters in the nearby spiral galaxy, M83, along with Hubble Space Telescope (HST) imaging in the optical and NIR, and ground-based NIR imaging, to see how the colours (and hence estimated properties such as age and extinction) are affected by the aperture size employed, in order to simulate studies of differing resolution. We find that the NIR is heavily affected by the resolution, and when aperture sizes >40 pc are used, all young/blue clusters move redwards in colour space, which results in their appearance as heavily extincted clusters. However, this is due to contamination from nearby sources and nebular emission, and is not an extinction effect. Optical colours are much less affected by resolution. Due to the larger effect of contamination in the NIR, we find that, in some cases, clusters will appear to show NIR excess when large (>20 pc) apertures are used. Our results explain why few young (<6 Myr), low-extinction (A V <1 mag) clusters have been found in recent ground-based NIR studies of cluster populations, while many such clusters have been found in higher resolution HST-based studies. Additionally, resolution effects appear to (at least partially) explain the origin of the NIR excess that has been found in a number of extragalactic young massive clusters.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014 RAS, MNRA Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 27 Nov 2014 11:30
Last Modified: 17 Apr 2015 11:49
URI: http://researchonline.ljmu.ac.uk/id/eprint/210

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